The long-distance optical transport network with wavelength-division multiplexing (WDM) technology has shown a promising future for high-capacity optical fiber communications. In such a network, the communications between central offices within a telecommunications network are conveyed by a fiber-trunk mesh. Each central office acts as a network node, where signals from different fiber trunks and local client offices are either switched to different output fiber trunks for transmission to the next node, or dropped to the local offices.
The Wavelength Selective Cross-Connect (WSXC) is one type of known optical cross-connect. WSXC accepts multiwavelength signals and cross-connects individual wavelengths. Received signals are wavelength demultiplexed and then the signals having the same wavelength are switched on a wavelength-specific switching layer. In a WDM system, each WDM channel will be associated with a unique WSXC switching layer. At a network node connecting P fibers each having Q wavelength channels, the WSXC will have Q P-by-P switching layers. WSXC is nonblocking in any wavelength-specific layer, but is blocking from one wavelength layer to another. In other words, a signal received on any input port for a given wavelength-specific layer can be switched to any output port for that layer. A signal received on an output port of a given wavelength-specific layer, however, cannot be switched to an output port of a different wavelength-specific layer.
Another type of known optical cross-connect is the Wavelength Interchanging Cross-Connect (WIXC). WIXC accepts multiwavelength signals and cross-connects signals with wavelength interchange when necessary. In other words, at a network node connecting P fibers each having Q wavelength channels, the WIXC will have a single PQ-by-PQ switching layer. WIXC is nonblocking between fibers and between wavelength layers.
With network traffic demand rapidly growing, there is a growing demand for increased capacity in a telecommunications network. A likely solution to increase the capacity of a telecommunications network is to increase the number of wavelengths in WDM systems and/or to increase the quantities of fibers in each fiber trunk. This solution requires the high-capacity switch fabrics at the central offices to handle an increased number of input/output ports. Consequently, an optimum switch architecture should have a manageable switch size and have high expandability.
Known optical cross-connects, however, cannot adequately address the increased capacity requirements of telecommunications networks having rapidly growing traffic. Known optical cross-connects must increase the number of ports in the switch layers as the number of wavelengths and/or the quantities of fibers in each fiber trunk increases. Specifically, in the WSXC, the number of ports in each switching layer must be increased as the quantity of fibers in each fiber trunk increases. Similarly, in the WIXC, the number of ports in the single switching layer must be increased as either the number of wavelengths or the quantities of fibers in each fiber trunk increases. At some point, cost and/or available technology prohibits adding more ports to a switching layer to expand the capacity of known optical cross-connects. Consequently, known optical cross-connects have limited expandability and create management problems as capacity requirements increase.